Cylindrical rollers and pulleys find many uses, for example as pulleys or guide or drive rollers in letter extracting or sorting machines, as pulleys or idlers in flat belt drive systems, or as rollers in beltless or belted conveyor systems to list just a few basic uses. Examples of some of these applications are shown in FIGS. 1A, 1B and 1C, 2 and 3. Applications of these basic types of uses illustrated in FIGS. 1A, 1B and 1C, 2 and 3 may be found in many variations. The shape of the roller may be crowned or “barrel-shaped,” straight sided, or having a cone profile or other cross-section depending on the application. A crown profile provides self-alignment or self-tracking of the flat article of belt in contact with the roller; a straight profile is suitable when the alignment is otherwise provided in the application.
Referring to FIG. 1A, there is illustrated a top view of a pair of rollers shown in a typical application of moving a thin planar object in the direction of the arrow. One or both of the rollers may be driven and the rollers may have a straight cylindrical cross-section or they may be crowned. A first roller 10 rotates on an axle assembly 12 about a longitudinal axis 14 in the direction shown by arrow 16. Similarly, second roller 18 rotates on axle assembly 20 about the longitudinal axis 22 in the direction shown by arrow 24. A thin planar object 26 such as a letter in a mail sorting machine encounters the pair of rotating first and second rollers 10, 18 and is caused to move in the direction of arrow 28 which is a common operation in a mail sorting machine.
FIG. 1B illustrates the apparatus of FIG. 1A from an end view taken through section A′—A′ wherein the thin planar object 26 is moving in a direction out of the page toward the viewer. In FIG. 1B the first roller 10 and the second roller 18 are each shown as having a crowned surface shape. This shape is typically used in applications to provide a self-aligning action as the rollers impart the moving force to the thin planar object or letter 26 by the action of the rotating rollers 10, 18. The axle assemblies 12, 20 shown in FIGS. 1A and 1B are greatly simplified and represent a wide variety of axle assemblies both driven and passive that may be found in such applications. Several of these axle assemblies will be illustrated and described in detail hereinbelow.
FIG. 1C illustrates a perspective of one example of a letter transport belt-and-pulley system which utilizes rollers or pulleys as described herein. A deck plate 11 includes two subsystems of a flat belt 15 disposed around a series of pulleys 13. One or more of the pulleys 13 are driven and the remaining pulleys 13 are roller pulleys. The belts 15 are driven in the direction shown by the arrows 17, which causes a letter 19 to be transported in the direction 21.
FIG. 2 illustrates a perspective view of a flat belt and pulley system using a pair of crowned rollers. A first crowned roller 30 rotates about an axle assembly 32 and a second crowned roller 34 rotates about an axle assembly 36. A flat belt 38 installed upon the pair of crowned rollers will remain in alignment on the pulleys because of the crowned profile of the pulleys when one of the pulleys is rotated by a motive force (not shown). The concept of a flat belt pulley system as illustrated in FIG. 2 is found in many applications in industrial facilities and machinery. It may also find widespread use in conveying systems, in farming and other manufacturing applications.
FIG. 3 illustrates another application that utilizes a roller as an idler pulley in a serpentine belt drive system such as is found on automotive engines. There, the single belt is used to operate various accessories such as a water pump, a generator or alternator, a power steering pump or an air conditioning compressor and the like. The belt, illustrated in FIG. 3 as a flat belt, is disposed around first, second and third pulleys 40, 42 and 44 respectively as well as an idler pulley 46 which rotates on axle assembly 48. The idler pulley 46 may be a cylindrical roller of the type shown in FIGS. 1 or 2 and which will be discussed in detail hereinbelow. In the illustrated application, the idler pulley is used for maintaining the belt tension in a multiple pulley system.
In FIG. 4, a prior art roller shown in cross-section with respect to a centerline through the axle assembly is illustrated. In FIG. 4, a roller 52 is mounted on an axle assembly 54 which is installed in a hollow cylindrical space 68 within the roller 52. The axle 54 is supported within the space 68 along centerline 56 by a pair of ball bearings 58 which are set against shoulders 64 machined into the ends of the roller body 52 and retained by opposing pairs of conical washers 60 held in a compressed configuration by the retaining rings 66 on each end of the axle bearing assembly 54. The conical washers provide the pre-loading necessary for smooth operation. In FIG. 4, the conical washers 60 are disposed as one pair on each bearing to provide center loading of the bearings 58. The ball bearings 58 are of conventional type and are readily available through a number of suppliers.
The type of prior art roller shown in FIG. 4, often found in the applications such as FIGS. 1A, 1B and 1C, 2 and 3, typically formed by molding, die casting or machining from solid bar stock or thick walled tube stock from materials such as steel, aluminum, brass or even stainless steel. In the case of die casting, the materials most often used are aluminum or zinc whereas for molded pulleys or rollers, plastic materials may be used. In the case of aluminum or zinc or plastics used as the material for fabricating the roller, these materials lack surface hardness or resistance to pitting or other damage without special treatments that add to their cost. Further, plastic rollers or pulleys are electrically non-conductive and therefore tend to accumulate static electrical charge which can be hazardous because of the risk of fire if flammable materials are nearby. Static charge can also attract and accumulate dust which is an impairment to the performance of the pulley and belt systems. Of these materials, the aluminum provides good electrical conductivity and is very light in weight. However, its relatively poor wear resistance is a drawback to its use. Rollers which have a high wear resistance as well as durability and electrical conductivity are typically made out of steel. However, steel is a heavy material and usually requires a surface coating or plating to protect it from rust or corrosion. Stainless steel provides the resistance to rust and corrosion but is also heavy and is significantly more expensive than the other materials.
Referring further to FIG. 4, each pair of conical washers 60 is used by placing one washer with its concave side facing the concave side of the other washer, the combination being held in compression by the retaining ring 66 which clamps the pair of conical washers on each side of bearing 58 against the inner race of the bearing 58. In other applications, one of the pairs of conical washers 60 may be eliminated to provide single ended loading to the axle assembly. The roller 52 of FIG. 4 is shown as having a solid body which is typical of prior art rollers or pulleys of the cylindrical configuration. As described hereinabove, the roller is typically formed by molding, die casting or machining from solid stock and the cylindrical space along the centerline 56 is provided by boring or other machining operations to provide the particular configuration needed to retain the bearing assembly for a specific application. Among the disadvantages of the prior art roller shown in FIG. 4 are its weight, its relatively high cost of manufacture and its poor resistance to corrosion and wear without special additional surface treatments. The weight is a factor because the inertia of the rotating mass places a greater load upon the driving machinery such as electric motors. Thus, benefits to be gained by lower mass in the roller assembly include smaller motors used to drive the machinery as well as less electricity to operate the motors. Lower mass also results in reduced stress and wear on bearing assemblies and upon belts used with the rollers or pulleys.
To summarize, prior art cylindrical rollers are used in a wide variety of sizes, shapes and materials. Rollers intended for industrial or long term uses are typically machined, or cast and machined, from solid stock for durability. In letter sorting machines for example, rollers may be solid aluminum which provides light weight and relatively light loading on the drive rotors especially when accelerating or decelerating, etc. However, aluminum requires a surface plating or other treatment such as hard anodizing to inhibit corrosion and provide improved resistance to denting and other surface damage because of its inherent lack of hardness. Plated steel or stainless steel provides the necessary corrosion resistance and surface durability for cylindrical rollers and pulleys but these materials are relatively heavy and require stronger supporting structure and drive motors as well as greater energy requirements for their operation. Solid metal of most common and practical materials are also noisy in operation because of their natural resonance, i.e., they “ring,” and because their greater mass places greater loads on the drive apparatus. Solid rollers or pulleys are also expensive to manufacture because of the relatively high cost of casting and machining. In many applications the rollers must be metallic in order that accumulation of static electric charge may be prevented.
What is needed therefore is a lightweight roller or pulley that is manufactureable at very low cost yet very durable, quiet in operation, resistant to static electricity accumulations and is adaptable to a wide variety of applications.